Electrical instruments traditionally have been assembled within dedicated housings or packages. Such instrument containment devices have been designed, for example, to be rack mounted or to stand alone upon a surface and conventionally have included a dedicated power supply, environmental components such as fans, filters, and the like, functioning to support electronic circuitry. Over the somewhat recent past, both government and industry have recognized the practicality and thus desirability of combining electronic modules having a variety of different, but facility related functions within a singular enclosure. Thus, a centralized support component assemblage including a power source, environmental controls and the like would be combined within a singular enclosure or envelope. These common support components then would service discrete instrument functions which, in turn, would be provided upon more elemental circuit boards which would be, in turn, standardized for insertion and support within the common container. Such circuits are generally referred to now as cards or modules.
The entity established to evolve the specifications for this standardized enclosure is known as the VXI consortium, the term VXI being an acronym for: "VME bus extensions for instrumentation". Within that acronym, the term "VME" represents a back plane/bus structure referred to as "Versa Module Eurocard" developed by Mostek and Signetics Incorporated. Thus, the VXI specification incorporates a standardized back plane referred to as a "VME/VXI" back plane.
Standardization specifications have been developed by the VXI consortium, for instance, a third iteration thereof being promulgated and referred to as the "VXIbus Specification Rev. R1.3." In addition to system environmental requirements concerning air flow and the like, the specification calls for the provision of a sequence of power source derived voltage outputs, each of which, is called upon to remain within defined tolerances. In the latter regard, voltages of -2 vdc, +5 vdc, -5.2 vdc, +12 vdc, -12 vdc, +24 vdc, and -24 vdc, are called for within strictly defined tolerances. Additionally, a +5 v stand-by source is called for. To the present time, enclosure fabricators have provided the required power sources and air driving components in conjunction with card racks and the like. However, users of the system when combining cards or modules within the enclosures and associated support systems, have been left without a continued assurance that all support systems remain within the VXI mandated performance or output specifications. Considering that several individual cards or modules may be combined within a common VXI specified enclosure and that each may have a value ranging, for example, from $5,000.00 to $20,000.00, it is desirable that any risk of module or card damage or destruction be minimized to the extent possible. For example, should undetected shorts or the like occurring within the wired components evoke a change in voltage from one source to another, for example, from -2 vdc to +24 vdc, card based circuit destruction may be inevitable. Additionally, should the air filtering systems of the enclosures be blocked or not be maintenanced by cleaning or replacement, or should associated fans driving circulating air malfunction, heat excursions may take place occasioning the damaging or destruction of expensive circuit modules. In general, technical personnel called upon to assemble a card array within a VXI defined enclosure desire an assurance that all support systems are performing within the VXI bus mandated tolerances.
Enclosures heretofore introduced to the market under the aegis of the VXI specification also have posed accessing difficulties to the user. Typically, the procedure for the otherwise simple task of changing filters within air circulation systems has called for rather elaborate dissasembly and reassembly activities. User access to components within the enclosures has been difficult, again usually calling for disassembly/assembly routines on the part of servicing personnel. In effect, while the advantages of stringent specifications of environment and power source components has demonstrated the desirability of this common enclosure approach, the assurances of proper performance and practical assessability in the use of the devices heretofore has not been entertained. The enclosures have exhibited a practical "awkwardness" making them unduly cumbersome to use and access in the field.